This invention relates to an intrauterine pulse oximetry apparatus and method for measuring fetal oxygen saturation during labor and delivery. The invention particularly relates to placing the apparatus within a preferred region on the fetus.
A fetal pulse oximetry apparatus may include a sensor attached to an electrical cable. The sensor, which contains a light source and a light detector, is placed on the fetus. The cable connects the sensor to a pulse oximeter. Light from the light source is transmitted through the fetal tissue and reflected back to the light detector. The amount of light received by the light detector depends on characteristics of the blood in the fetal tissue, among other things.
Fetal pulse oximetry sensors are not new. Some previous apparatus were physically attached to the fetal skin by hooks, spirals, suction, or glue. One example is the fetal pulse oximetry sensor disclosed in PCT Publication No. WO 90/01293. These attachment means were invasive or potentially harmful. Therefore the apparatus were placed only in fetal regions that the doctor or other user could reach with his or her fingers, such as on the presenting part of the fetus or on the fetus within the uterine region just beyond the cervix (the "transcervical region").
The structure of previous apparatus did not permit safe and accurate placement on the fetus in the region beyond the reach of the user. In addition, nothing was known of fetal pulse characteristics in this region. Thus placement of the apparatus beyond the presenting part or in the transcervical region was considered undesirable.